1. Field of the Invention
This invention relates to a cyclohexane derivative, and more particularly it relates to a phenyl-4-cyclohexylbutylcyclohexane derivative and a liquid crystal composition containing the same as an effective component.
2. Description of the Related Art
Liquid crystal display elements utilize the optical anisotropy and dielectric aniostropy of liquid crystal substances, and as their display modes, TN mode (twisted nematic mode), super-twisted, nematic mode (STN mode), dynamic scattering mode (DS mode), guest-host mode (G.H. mode), DAP mode, etc. have been known. Further, as the driving mode thereof, static driving mode, multiplex driving mode, active matrix driving mode, two-frequency addressing scheme, etc. have been employed. The properties of the liquid crystal substances required for these various liquid crystal display elements are varied, but any of these liquid crystal substances are commonly required to be stable to moisture, air, heat, light, etc. and also required to exhibit liquid crystal phases within a mesomorphic range as broad as possible around room temperature, have a low viscosity, and exhibit a quick response, a high contrast and further a low driving voltage in the display elements, and also required to have a superior compatibility with other liquid crystalline compounds since the substances are usually used as compositions. Further, it is required to have the optimum dielectric anisotropy value (.DELTA..epsilon.) depending upon the kinds of display elements. However, no liquid crystal compound satisfying these specific features as a single component has been known at present. Hence, it is the present status that liquid crystal compositions obtained by blending several liquid crystalline compounds or non-crystalline compound have been used.
As described above, since a mixture of liquid crystalline compounds are used for compositions, the compatibility thereof is important, and in particular, the compatibility at low temperatures is one of the most important factors for liquid crystal display elements wherein driving within a broad temperature range is required.
As conventional liquid crystal compounds, the following compounds have been disclosed: ##STR2##
Compound of (I) U.S. Pat. No. 4,405,488 has a structure wherein two cyclohexane rings and a benzene ring are directly bonded, and compounds of (II) and (III) have an ethane bond in the molecule, respectively. It has been generally known that the ethane bond linking the core parts (mainly cyclohexane ring and benzene ring) of usual liquid crystal molecules has an effect of retaining the compatibility at low temperatures without raising the viscosity, but even in the case of compounds having the same ethane bond, when the case of linking cyclohexane ring and benzene ring (compound (II)) is compared in the aspect of properties, with the case of linking cyclohexane ring and cyclohexane ring (compound (III)), the result is different. Namely, in the case of compound (III), a sufficient effect of low temperature compatibility can be obtained by inserting the ethane bond, as compared with the case of compound (I), whereas in the case of compound (II), the effect is insufficient. Further, Japanese patent application laid-open No. Hei 3-66632 discloses the following compound wherein cyclohexane ring and benzene ring are linked by a linear butane bond: ##STR3##
In the case of compound (IV), according to the report of its properties, its smectic properties are strong, and the effect of compatibility by butane bond inserted as a linking group for cores of a liquid crystalline molecule, with other liquid crystalline compounds, particularly at low temperatures, is insufficient.
Thus, the present inventors have investigated introduction of an alkyl group into the core-linking part of the liquid crystalline molecule, and as a result, have found that when two cyclohexane groups are linked with butane bond, the smectic phase is suppressed, the nematic phase is broadened and also the compatibility at low temperatures is improved. Thus, the compounds recited in the instant claims as novel liquid crystalline substances have been invented.